T lymphocyte derived cell lines, including cytolytic T lymphocyte (CTL) clones possessing stable lytic activity, will be established from mouse lymphocytes. Subsequently, variant CTL lines having full, partial, aberrent and null lytic activity will be derived using mutagenizing agents. Two approaches will be used for obtaining variant CTL lines. The first approach will use a panel of monclonal antibodies and complement to select antigenic-loss variants deficient in lymphocyte surface antigens such as LFA-1, Lyt2/3, H-2, Thy-1, and T-200. The second approach will select functional variants by screening for altered lytic activity using 51Cr release assays, and may result in variants deficient in as yet unidentified molecules, such as the receptor and lysin. Antigenic-loss variants which have lost LFA-1 or Lyt-2/3 determinants, or molecules, if they retain normal function, will exclude a direct role for these moieties in killing. For variants showing aberrent activity we will determine the affected step: motility, recognition, post-recognition adhesion, and/or programming for lysis. With quantitative flow cytofluorometry and monoclonal antibodies we will analyze antigenic phenotypes of clones. The molecular nature of altered molecules will be studied by comparing membrane preparations from variant, parental, and non-CTL lines using a number of techniques such as immunoprecipatation, SDS-PAGE, isolectric focusing and 2-dimensional gels. By correlating the presence or absence of discrete CTL activities, such as, motility, recognition, adhesion, and programming for lysis, with mutations affecting cell surface molecules, we expect to identify and characterize molecules involved in CTL-mediated killing.